In an automatic embroidery sewing machine, embroidering data are stored in a memorizing medium such as a floppy disc etc., and signals of said data are read out by a phase signal per each rotation of the sewing machine, and two electromagnetic actuators which provide control in an X direction and control in a Y direction, are driven in accordance with said signal at a phase where a needle is above a fabric to be stitched, to provide X and Y controls on the embroidery frame and form stitches on the fabric supported by the embroidery frame. The above mentioned conventional embodiments are roughly classified into the following two kinds.
a. The needle reciprocates vertically only without moving in amplitude, and PA1 b. The needle moves in amplitude and vertical reciprocation.
When an embroidering pattern is, as shown in FIG. 1(a), produced by the automatic embroidery sewing machine of the above (a) type, the embroidery frame having large quality and quantity of inertia should be moved in the X and Y directions concurrently in accordance with signals of said pattern stitching data within a certain phase where the needle is above the fabric. Therefore, the maximum rotation speed of the sewing machine is limited to about 600 rpm due to the responding limit of said electromagnetic actuator, resulting in a problem involving working efficiency.
Further problems are large vibrations and noises caused by the quality and quantity of the inertia of the embroidery frame even in the lower rotation speed.
In addition, rapid movement as mentioned above is not preferable in view of durability, and generates play in members composing the device that drives the embroidery frame consequently making vibrations and noises larger, so that stitched patterns are deformed, and responsibility is underestimated in view of the durability in the members.
An automatic embroidery sewing machine of the above (b) type is to improve each of the above mentioned problems involved in the (a) type. A zigzag generator of the automatic embroidery sewing machine of the (b) type is composed in outline as seen in FIG. 2. In FIG. 2, a triangular cam 1 is fixedly mounted on a shaft 2 which has 1/2 the rotation speed of an upper shaft of the sewing machine. A fork member 3 to be turned by the angular cam 1 is controlled by a controller 5 which is obliquely controlled by a zigzag width control motor 4, and gives zigzag action to a needle bar supporter 6 and a needle bar 7.
Since the zigzag width control motor 4 does not directly turn the needle bar 7 but indirectly controls it by changing the obliqueness of the controller 5 when the zigzag width is changed, the motor 4 has the equivalent value to controlling members of smaller inertia, and especially letters which in the embroidering patterns do not require rapid changings in the embroidering width and the motor 4 could follow the high speed rotation of the sewing machine.
For producing the stitching pattern as shown in FIG. 1(a) by the automatic embroidery sewing machine of the (b) type, if X and Y directions are determined and the zigzag direction is made in Y direction, it is sufficient that the needle moves relatively and straightly on the center of the embroidery width, and the movement of the embroidery frame may be reduced as small as possible. Therefore this kind of the automatic embroidery sewing machine could follow a high speed of around 2000 rpm, and the durability of the driving device of the embroidery frame is satisfactory.
Unfortunately, the automatic embroidery sewing machine of the (b) type could not satisfy varieties of stitchings. For producing the embroidering patterns of a shape as shown in FIG. 1(b), it is not preferable to limit stitching shapes in spite of various stitchings, and in the present case consideration is taken with regard to formation of the pattern shown in FIG. 1(b). Herein, a problem arises regarding the case of composing stitchings oriented in directions varying by 90.degree.. As the obliquness between a standard direction (i.e. Y direction and same direction as the zigzag direction) and the stitching direction becomes larger, the zigzag movement is not available. Especially, when the standard direction and the stitching direction are at an angle 90.degree. from each other as seen in a lateral part of "T" in FIG. 1(b), the needle is in the same effect in the straight movement, and the embroidery frame should be moved at the small distance in the Y direction and at the large distance in the X direction per each of stitchings. Therefore, in the stitching condition, this is the same as the (a) type sewing machine and could not follow the high rotation of 2000 rpm, and if rotation were 600 rpm as the (a) type, the same problems would appear as therein.